Storage Devices
Categories of Media
Four Categories of storage media:
- Magnetic media
- Hard Disks and Tapes
- Non-volatile memory (flash)
- Optical media.
Partitioning and Slack Space
Interfaces
SATA (Serial Advanced Technology Attachment)
- Versions/Speeds
- 1.5 Gb/s for SATA 1
- 3.0 Gb/s for SATA 2
- 6 Gb/s (~700MB/s) for SATA 3
- 16 Gb/s for SATA 3.2
- has card-edge connector
SAS (Serial Attached SCSI)
- Versions/Speeds
- 3 Gb/s for SAS 1
- 6 Gb/s for SAS 2
- 12 Gb/s for SAS 3
- 22.5 Gb/s for SAS 4
- Same connector/interface as SATA, but has separator
SCSI (Small Computer System Interface)
- aka Scuzzy
- up to 320 Mb/s
- SCSI-2: 50-pin interface, Molex power
- SCSI-3: 68-pin interface, Molex power
- SCSI-3 variant: 80-pin interface
IDE (Integrated Drive Electronics) aka PATA
- 133 Mb/s
- has pin connector
- 40-position connector; 39-pin interface
- IDE drive jumper options
- Master
- Slave
- Cable select
- Note original jumper setting prior to imaging
- Standard power connector
HDD Disk Parts/Design
HDD Sizes
HDDs has 3 storage sizes:
- 3.5 in
- 2.5 in
- 1.8 in
Components
Parts of a drive:
**
Disk Data Structure
Platters
- round flat, magnetic or ceramic discs in a hard drive that holds the actual data
- Made of two materials
- Substrate Material
- Magnetic Media Coating
- Each platter has two sides
- sides are numbered starting at 0
- Most drives have multiple platters
- Made of two materials
Tracks
-
Each platter has tracks, which is where data is stores
- Most platters have 10k+ tracks
- Track numbering start at 0 from the outside
- Stacks of tracks are called cylinders
-
Number of cylinders (tracks), heads (sides), and sectors (aka CHS) uniquely identify the physical geometry of the storage units on a disk
- CHS also yields disk capacity:
- Capacity = Cylinders x Heads x Sectors x sector size
-
Trend toward less platters with more density
Sectors
- Each track has sectors
- 1 sector = 512 bytes (sometimes 4096) and a few extra "info bits"
- Info bits include ID info, synchronization fields, and ECC data.
- Sectors can turn bad beacuse of:
- excessive read/writes
- some viruses
- voltage surges
- Drives have reserved sectors, which are used as others fail
- bad sectors are difficult to see by normal operating systems, requires special hardware
- 1 sector = 512 bytes (sometimes 4096) and a few extra "info bits"
Fragmentation
- Data on HDDs can be spread out, called fragmentation.
- Fragmentation increases seek time/delay
SSD Parts/Design
Components
- SSDs use flash based storage and a controller
Advantages over HDDs
- Constant seek time
- No file fragmentation issues
- No moving parts
- no mechanical failures
- fast startup time
- no motor noise
- Lighter weight
- low power
Issues
- Overwriting process is complicated & expensive
- read-erase-modify-write cycle
- Cells have limited life/cycles
- Wear leveling must be used
- SSDs are significantly harder to save data from
SSD Data storage structure
- 1 page = 8 sections/sectors (512 bytes)
- Pages make up blocks
Data writing process
- Write is fast
- But rewrite/overwrite involves additional erasing step
- Entire Blocks (not pages or sections) must be erased
- Grey = unused page
- blue = in-use page
- Optimization strategies
- Garbage collection
SSD Lifespan
- Individual memory cells have limited read/write cycles (5000 – 50000)
- Like hard disks SSDs have extra capacity not accessible by normal users
- Unlike hard disks Approx. 10-25% more storage than stated capacity, Overprovisioned areas are continuously used
TRIM
- File Deletion on a normal HDD
- File is marked as deleted in the File system’s database
- HDD has no clue which sectors are freed up
- TRIM marks data blocks as stale
- SSDs need to know this info.
- Modern OS have support for this command